Processes for cationically polymerizing olefins are known in the art. U.S. Pat. No. 6,858,690 to Webb et al. discloses a method of making butyl rubber wherein processing efficiency including heat transfer is improved by utilizing a tertiary halogen initiator. See, also, U.S. Pat. No. 3,932,371 to Powers which discloses polymerization of copolymers of isoolefins and conjugated dienes in a two-phase system where propane is used as a diluent in order to improve heat transfer.
The polymerization of olefins using Friedel-Crafts type catalysts, such as boron trifluoride and aluminum trichloride is well known. The degree of polymerization of the products obtained varies according to which of the various known polymerization techniques is used and also varies with the parameters used to control the reaction. The molecular weight of the polymeric product is directly related to the degree of polymerization and that the degree of polymerization may be manipulated by manipulating process parameters so as to produce a variety of products having respective desired average molecular weights. Due to the nature and mechanics of the olefinic polymerization process, a polyolefin product has a single double bond remaining in each molecule at the end of the polymerization process. The position of this remaining double bond is often an important feature of the product. For example, polyisobutylene (PIB) molecules wherein the remaining double bond is in a terminal (vinylidene) position are known to be more reactive than PIB molecules wherein the remaining double bond is internal, that is, not in a terminal position. A PIB product wherein most of the double bonds are in a terminal position may often be referred to as high vinylidene or reactive PIB. The extent to which a polyolefin product has terminal double bonds may also be manipulated by manipulation of process parameters.
It is also known that alpha olefins, particularly PIB, may be manufactured in at least two different classes of material—regular and high vinylidene. Conventionally, these two product grades have been made by different processes, but both often and commonly use a diluted feedstock in which the isobutylene concentration may range from 40 to as high as 90% by weight. Non-reactive hydrocarbons, such as isobutane, n-butane and/or other lower alkanes commonly present in petroleum fractions, may also be included in the feedstock as diluents. The feedstock often may also contain small quantities of other unsaturated hydrocarbons such as 1-butene and 2-butene.
High vinylidene, or highly reactive PIB, a relatively new product in the marketplace, is characterized by a large percentage of terminal double bonds, typically greater than 70% and preferentially greater than 80%. This provides a more reactive product, compared to regular PIB, and hence this product is also referred to as highly reactive PIB. The terms highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HR-PIB all include a reactor system, employing BF3 and/or modified BF3 catalysts, such that the reaction time can be closely controlled and the catalyst can be immediately neutralized once the desired product has been formed. Since formation of the terminal double bond is kinetically favored, short reactions times favor high vinylidene levels. The reaction is quenched, usually with an aqueous base solution, such as, for example, NH4OH, before significant isomerization to internal double bonds can take place. Molecular weights are relatively low. HR-PIB having an average molecular weight of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization. Prior U.S. Pat. No. 4,152,499 dated May 1, 1979, prior U.S. Pat. No. 4,605,808 dated Aug. 12, 1986, prior U.S. Pat. No. 5,068,490 dated Nov. 26, 1991, prior U.S. Pat. No. 5,191,044 dated Mar. 2, 1993, prior U.S. Pat. No. 5,286,823 dated Jun. 22, 1992, prior U.S. Pat. No. 5,408,018 dated Apr. 18, 1995 and prior U.S. Pat. No. 5,962,604 dated Oct. 5, 1999 are all directed to related subject matter.
Other than the HR grades and the regular grades of PIB, a certain grade of PIB known as the enhanced grade has been more recently developed (EP 1381637 and related patents discussed below). The advantage of these series of products is that the overall reactivity is high without the need for high vinylidene content.
The present invention is directed, in part, to controlling the reaction in a loop reactor by lowering the diluent content and manipulating the tube velocity and recirculation rate of the process fluid. The invention is particularly concerned with polymerization of isobutylene and includes significant improvements to existing technology in terms of diluent content, conversion, product attributes and so forth discussed in more detail below.
U.S. Pat. No. 6,844,400 shows an apparatus for polymerizing isobutylene wherein the recirculation rate is specified in the range of 20:1 to 50:1 and notes that higher recirculation ratios increase the degree of mixing, leading to narrower polymer distributions. Col. 9, lines 37-59. The '400 patent teaches to use two reactors in order to increase the conversion and to use lower flow rates to increase the residence time. Col. 11, line 57 to Col. 12, line 11. Related patents include U.S. Pat. Nos. 6,777,506 and 6,858,188. These patents all teach to increase residence time in order to increase conversion and lower polydispersity. See, also, U.S. Pat. No. 7,038,008 which discloses recirculation rates of 1000:1 to 1:1. See Col. 3, lines 55-64.
In U.S. Pat. No. 7,645,847 it is noted a Reynolds Number of at least 2000 is desirable in a tube and shell reactor for making isobutylene. Col. 8, lines 26-36, as well as a recirculation rate of from 20:1 to 50:1, Col. 5, lines 54-64. Single reactor conversion rates are disclosed at 51% in Table 6 for a residence time of 58 seconds. The '847 patent mentions:                The molar ratio of BF3 to complexing agent in the catalyst composition may generally be within the range of from approximately 0.5:1 to approximately 5:1, desirably within the range of from approximately 0.5:1 to approximately 2:1, and preferably within the range of from approximately 0.5:1 to approximately 1:1. Ideally, the catalyst composition may simply be a 1:1 complex of BF3 and methanol. In some preferred embodiments of the invention, the molar ratio of BF3 to complexing agent in said complex may be approximately 0.75:1. Col. 10, lines 14-23and that:        Generally speaking, for PIB production the amount of the BF3 catalyst introduced into the reaction zone should be within the range of from about 0.1 to about 10 millimoles for each mole of isobutylene introduced into the reaction zone. Preferably, the BF3 catalyst may be introduced at a rate of about 0.5 to about 2 millimoles per mole of isobutylene introduced in the feedstock. Col. 10, lines 36-43.Conversion levels are conventionally inversely related to α-vinylidene content. Col. 14, lines 35-47. See, also, U.S. Pat. No. 6,992,152 which notes temperatures of at least 0° C. up to 60° F. or higher. Note U.S. Pat. No. 6,884,858, Example 2, where the reaction temperature is maintained at 90° F. Process parameters appear in Table 4 of the '858 patent, Col. 15, including a Reynolds Number reported at 3180 and a recirculation rate of 50/1.7 or 29.4. Related patents include U.S. Pat. No. 6,525,149; U.S. Pat. Nos. 6,683,138; and 6,562,913.        
The following patents describe mid-range vinylidene content polyisobutylene (PIB) polymers and processes for producing them: U.S. Pat. Nos. 7,037,099; 7,091,285; 7,056,990; and 7,498,396. The products are characterized in that at least about 90% of the PIB molecules present in the product comprise alpha or beta position isomers. The vinylidene (alpha) isomer content of the product may range from 20% to 70% thereof and the content of tetra-substituted internal double bonds is very low, preferably less than about 10% or 5% and ideally less than about 1-2%. The midrange vinylidene content PIB polymer products are prepared by a liquid phase polymerization process conducted in a loop reactor at a temperature of at least 60° F. using a BF3/methanol catalyst complex and a contact time of no more than 4 minutes. Otherwise, processing is similar to the other patents noted above.
Prior art systems are characterized by diluents content in the reaction mixture of 10 percent by weight or more and oftentimes by 50% by weight diluents and more, requiring solvent recycle and/or involving high solvent costs. Likewise, prior art systems are typically characterized by linear velocity in reactor tubes of less than 10 ft/sec as is seen in European Patent No. EP 1 242 464. Note particularly Table 4 where a linear velocity of 9.3 ft/sec is specified as well as Tables 6 and 8 where linear velocities of 6.59 ft/sec appear.